A back-lighting device in a general liquid-crystal display apparatus mainly includes a light source, a light-guiding plate (light-guiding film) that guides light from the light source; a reflective sheet that reflects light passing through the light-guiding plate, a diffusion sheet for homogenizing light emitted from a light-emission surface of the light-guiding plate, and a prism sheet that enhances a luminance of the light in a perpendicular direction of the light-emission surface.
A method for manufacturing such prism sheet will be described. A conventional manufacturing apparatus 10, which is illustrated in FIG. 5, includes a die 1 that receives and extrudes a heated resin, a rectangular extrusion outlet 2 formed in the die 1, a main roll 3, and a follower roll 4. The main roll 3 and the follower roll 4 are disposed below the extrusion outlet 2 so as to sandwich a resin sheet 11 to be shaped therebetween, the resin sheet 11 being extruded from the extrusion outlet 2. In a surface of the main roll 3, microstructures for transferring prism shapes to the resin sheet 11 are formed.
The manufacturing apparatus 10 lets the heated resin sheet 11 through between the main roll 3 and the follower roll 4 and thereby shapes the resin sheet 11 into a prism sheet 12. In the shaping, as a result of the main roll 3 and the resin sheet being brought into contact with each other, a temperature of a surface of the resin sheet 11 decreases in area A of the main roll 3 illustrated in FIG. 5, and the resin sheet 11 thus becomes hard, which causes the problem of failure to accurately transfer the microstructures in the roll 3 to the resin sheet 11.
Therefore, in order to solve such problem, apparatuses including a mechanism that heats a vicinity of area A of the main roll 3 have been proposed. For example, Japanese Patent No. 5111800 describes a sheet molding apparatus in which a heating unit including a plurality of heat-transfer heaters is embedded in an outermost layer of a main roll 11 and the heat-transfer heaters are independently controlled, thereby preventing decrease in temperature of a resin sheet, as illustrated in FIG. 5 of Japanese Patent No. 5111800. Furthermore, Japanese Patent No. 5111800 also describes a sheet molding apparatus in which a radiation heating device such as a laser or a halogen lamp is provided outside a main roll to heat an outermost layer of the main roll 11, as illustrated in FIG. 6 of Japanese Patent No. 5111800.